The instant invention relates to current sources accurately adjustable by a voltage and more particularly the implementation of such current sources to digital/analog converters with high precision auto-calibration, for example of 12 bits,
In the prior art, in order to obtain digital/analog converters having a high precision and a great linearity, bipolar transistors associated with networks R-2R are used to form a set of switchable current sources, the values of which, with respect to the value of a reference current, form a geometric progression with a ratio 2. However, due to the manufacturing dispersions which impair the resistivity of the networks R-2R and of the bipolar transistors, it is compulsory, as soon as the number of bits of the digital/analog converter is over 7 or 8, to carry out a laser trimming of the resistors of the networks R-2R if a very high linearity is required. In the prior art, in order to obtain digital/analog converters having a high precision and a high linearity, without having to resort to the laser trimming of any component of the converter, various types of auto-calibration digital/analog converters, the adjustable components of which are capacitors, have been proposed; said capacitors belonging to a set of capacitors, the capacitances of which are referred to the capacitance of a unitary capacitor, form a geometric progression with a ratio 2.
An object of the instant invention is to provide for a simple current source, adjustable with a particularly high accuracy.
Another object of the instant invention is to provide for a digital/analog converter adjustable in an accurate way, making use of an adjustable current source and being therefore capable of comprising a large number of cells.
A further object of the instant invention is to provide for such a digital/analog converter particularly simple to manufacture and accurate when operating.